In the past, analysis using a particle size distribution measuring apparatus has been performed after diluting a sample with a solvent to obtain concentration exhibiting a predetermined transmittance. However, depending on a sample, the sample may be condensed or dissolved by dilution and lead to a change in state, and therefore there is a demand to measure the sample in an original undiluted state.
In order to measure a sample in an original undiluted state, it is necessary to use a cell having a short optical path length so as to make the sample have a predetermined transmittance. However, an undiluted sample often has high concentration and high viscosity, and therefore it is difficult to put the sample into a cell, and also clean the cell.
For this reason, in the past, by interposing a spacer between a pair of light transmitting plates, and sandwiching a sample between the pair of light transmitting plates, the thickness of the sample has been made uniform.
For example, Patent Literature 1 describes an optical analysis cell that includes a pair of glass plates and is configured by putting a sample into a concave part formed in one of the glass plates and then superposing the other glass plate on the one glass plate.
In the above-described configuration, this optical analysis cell is adapted to make the thickness of the sample equal to the depth of the concave part, and the thickness of the sample can be made seemingly uniform without the use of any spacer. However, in truth, the optical analysis cell is based on completely the same idea as the above-described conventional idea.
This is because as illustrated in FIG. 1, the thickness of the sample is determined by the thickness of a part around the concave part of the one glass plate, and the part can be regarded as a spacer.
In addition, in the above-described configuration, in the case where the amount of the sample is larger than the volume of the concave part, when superposing the two glass plates on each other, part of the sample protrudes from the concave part, and the protruding sample gets between the two glass plates. As a result, the two glass plates cannot be made parallel, and light cannot pass straight through them, giving rise to the problem that an optical axis cannot be accurately adjusted.
On the other hand, in the case where the amount of the sample is smaller than the volume of the concave part, the concave part cannot be filled with the sample, and therefore the thickness of the sample cannot be made uniform.
As described, the above-described optical analysis cell is not practical at all because in order to make the glass plates parallel to each other while making the thickness of the sample uniform, it is necessary to make adjustments so as to make the amount of the sample equal to the volume of the concave part.
Further, in addition to the above-described optical analysis cell, there is another optical analysis cell that is formed by interposing an elastic spacer between two light transmitting plates and configured to be able to utilize the repulsive force of the spacer to adjust the separation distance and parallelism between the light transmitting plates by pushing one of the light transmitting plates with multiple screws.
However, in the above-described configuration, only adjusting the separation distance between the light transmitting plates so as to make the thickness of a sample uniform is very delicate work. In addition, making adjustments so as to make the two glass plates parallel to each other is extremely difficult.